CN113517878A

CN113517878A - Implementation method and device for improving EMC (electro magnetic compatibility) of clock signal

Info

Publication number: CN113517878A
Application number: CN202110642293.3A
Authority: CN
Inventors: 康建政
Original assignee: XBO Medical Systems Co Ltd
Current assignee: XBO Medical Systems Co Ltd
Priority date: 2021-06-09
Filing date: 2021-06-09
Publication date: 2021-10-19

Abstract

The invention relates to a realization method and a device for improving clock signal EMC, which use a spread spectrum chip with a spread spectrum function, configure a proper resistance value at a configuration end of the chip to generate a spread spectrum clock signal, use the spread spectrum clock to replace the clock signal in an MRI system, and use the spread spectrum clock signal as an internal clock signal and an external clock signal in the MRI system, thereby improving the EMC radiation value. The beneficial effects are as follows: the device is simple in design and can be miniaturized, the device can be installed on any equipment of an MRI system or embedded into all circuit boards with clock signals, and the EMC radiation value of the clock signals is improved by using a spread spectrum technology; the conducted radiation limit is far exceeded in EMC testing relative to a device without this spread spectrum function. With this design added, there was a significant improvement in EMC radiation values in company MRI product certification, without exceeding the limits.

Description

Implementation method and device for improving EMC (electro magnetic compatibility) of clock signal

Technical Field

The invention relates to a realization method and a device for improving clock signal EMC, in particular to a realization method and a device for improving clock signal EMC of an MRI system, belonging to the technical field of clock signals.

Background

At present, the EMC test in the certification of the MRI equipment often has the condition of exceeding the standard, and the signals exceeding the standard are mostly caused by clock signals. In the circuit, clock signals are periodic signals, the periodic signals are narrow-band frequency spectrums, and the radiation value of a specific frequency is high, so that the EMC test is over-standard. This is very difficult to handle in rectification as soon as the clock signal radiation value exceeds a standard. At present, the method only adopts the modes of adding shielding, adding an EMC filter, high-low pass filtering and the like, which not only increases the cost, but also increases the debugging time, and sometimes the effect of the mode is not obvious.

Disclosure of Invention

The invention aims to provide a method and a device for improving EMC of a clock signal, which improve the EMC radiation value of the clock signal by using a spread spectrum technology, thereby perfectly solving the problem of radiation in EMC test generated by the clock signal of an MRI system.

The invention adopts the following technical scheme:

an implementation method for improving clock signal EMC comprises the following steps: a spread spectrum chip with a spread spectrum function is used, a proper resistance value is configured at a configuration end of the spread spectrum chip, the spread spectrum clock is used for replacing a clock signal in an MRI system, and equipment in the MRI system uses the spread spectrum clock signal as an internal clock signal and an external clock signal, so that the EMC radiation value is improved.

The adjustment range of the spread spectrum clock signal is 50kHz to 10 MHz;

the device for realizing the method consists of a spread spectrum chip and a matching resistor;

the spread spectrum chip adopts an LTC6908 spread spectrum chip of ADI company;

the spread spectrum range realized by the spread spectrum chip is +/-10%;

the matching resistance ranges between 100k omega and 20M omega.

The invention has the beneficial effects that: the device is simple in design and can be miniaturized, the device can be installed on any equipment of an MRI system or embedded into all circuit boards with clock signals, and the EMC radiation value of the clock signals is improved by using a spread spectrum technology; the conducted radiation limit is far exceeded in EMC testing relative to a device without this spread spectrum function. With this design added, there was a significant improvement in EMC radiation values in company MRI product certification, without exceeding the limits.

Drawings

FIG. 1 is a schematic diagram of the structure of the apparatus of the present invention;

FIG. 2 is a diagram comparing an original clock and a spread spectrum clock in the embodiment;

FIG. 3 is a graph comparing the amplitude of the original clock spectrum and the spectrum after spreading in the embodiment;

FIG. 4 is a graph of the spectrum (depth 2%, velocity 0.001) after 1Hz spreading in the example;

FIG. 5 is a graph of the spectrum (depth 1%, velocity 0.001) after 1Hz spreading in the example;

fig. 6 is a graph of the spectrum (depth 2%, velocity 0.0001) after spreading in the example.

Detailed Description

Example (b):

referring to fig. 1, an implementation method for improving EMC of a clock signal: a spread spectrum chip 1 using ADI with spread spectrum function LTC6908 is used, a matching resistor 2 with proper resistance value is arranged at the configuration end of the chip, and the chip is used as a device for improving clock signal EMC and is installed on any equipment of an MRI system or is embedded in all circuit boards with clock signals, so that a spread spectrum clock signal is generated, the spread spectrum clock is used for replacing the clock signals in the MRI system, and the equipment in the MRI system uses the spread spectrum clock signal as internal and external clock signals, thereby improving EMC radiation value.

The adjustment range of the spread spectrum clock signal is 50kHz to 10 MHz; the spread spectrum range realized by the spread spectrum chip is +/-10%; the matching resistance ranges between 100k omega and 20M omega.

The spread spectrum is to spread a narrow-band spectrum into a wide-band spectrum, so that energy is not concentrated to a certain frequency point, and the energy is dispersed to a plurality of frequency points. Therefore, the radiation problem in EMC test generated by the clock signal of the MRI system can be perfectly solved. This is also of value in the present invention.

As is known, a clock signal is usually a periodic signal, and its frequency spectrum is narrow-band and energy-concentrated. In order to widen the frequency spectrum of the clock signal, the clock signal must be modified, and each period of the original clock signal is the same, and the period time length is also the same and is Tclk. The fine tuning can be performed by, for example, first lengthening each clock cycle by a little more than the time of the previous clock cycle, accumulating 32 cycles, then shortening each clock cycle by a little more than the time of the previous clock cycle, accumulating 32 cycles, and so on. Thus, the number of clock cycles included in the total clock signal is constant, but each cycle of the clock signal is different, as shown in fig. 2.

From the above description, it can be seen that there are several parameters:

one is the modulation speed: i.e. 64 x Tclk, the inverse of which is the modulation frequency corresponding to the modulation speed.

One is modulation depth: after modulation, there will be the longest clock period and the shortest clock period, which have a difference with respect to the original period length, and this difference is divided by the original clock period, i.e. the modulation depth, which is a percentage.

Let the clock frequency be 1, the modulation speed be one thousandth of the clock, i.e. 0.001Hz, and the modulation depth be 2%. It can be seen from fig. 3 that the radiation value after spreading is significantly improved.

To see the spectrum after spreading more clearly, we close up the spread spectrum later as shown in fig. 4. The amplitude at 1Hz before modulation is 0.63 and the maximum amplitude after modulation is 0.15. If expressed in dB, then a 20log (0.63/0.15) =12.7dB reduction. Fig. 4 corresponds to a modulation depth of 2% and we reduce the modulation depth by 1%, looking again at the spectrum, as shown in fig. 5.

The spectral amplitude of fig. 5 with a modulation depth of 1% is at most 0.2, which, if expressed in dB, is a 20log (0.63/0.2) =9.96dB reduction.

Compared with the prior art, the larger the modulation depth is, the wider the frequency spectrum is, the smaller the amplitude is, and the better the suppression effect on EMC is.

If the modulation depth is not changed, the modulation speed is changed from 0.001 to 0.0001, namely, the modulation speed is reduced by 10 times, the modulation depth is 2 percent, and the frequency spectrum is shown in figure 6.

The spectral amplitude of fig. 6 is up to 0.05, which is a 20log (0.63/0.05) =22dB reduction if expressed in dB.

Claims

1. An implementation method for improving clock signal EMC is characterized in that: a spread spectrum chip with a spread spectrum function is used, a proper resistance value is configured at a configuration end of the spread spectrum chip, the spread spectrum clock is used for replacing a clock signal in an MRI system, and equipment in the MRI system uses the spread spectrum clock signal as an internal clock signal and an external clock signal, so that the EMC radiation value is improved.

2. An implementation method to improve clock signals EMC as claimed in claim 1, characterized by: the adjustment range of the spread spectrum clock signal is 50kHz to 10 MHz.

3. An apparatus for implementing a method for improving clock signal EMC as claimed in claim 1 or 2, characterized in that: the device consists of a spread spectrum chip and a matching resistor.

4. A method of implementing an improved clock signal EMC as claimed in claim 3, characterized in that: the spread spectrum chip adopts an LTC6908 spread spectrum chip of ADI company.

5. A method of implementing an improved clock signal EMC as claimed in claim 3, characterized in that: the spread spectrum range realized by the spread spectrum chip is +/-10%.

6. A method of implementing an improved clock signal EMC as claimed in claim 3, characterized in that: the matching resistance ranges between 100k omega and 20M omega.